Portable electronic devices, such as mobile cellular telephones, personal digital assistants (PDA's), digital cameras, portable audio devices (MP3 players, CD players, radios etc.) and portable video devices (recorders and players), are powered by electrical batteries. Large batteries are prohibitively heavy and/or bulky, so battery capacities are often around 1 amp hour (Ah), which provides an acceptable usage time for devices with low power consumption. Often these batteries are rechargeable.
Removeable batteries may be of standard size. This allows the batteries to be removed and placed in an external battery charger. However, many devices use custom sized batteries that are not removed from the electronic device for charging. For these devices, dedicated chargers are used. However, there is very little standardization of chargers, and consequently different brands of portable device and different types of portable device have different charges. A user may therefore be required to have a range of different chargers, all competing for space and electrical power outlets. The problem is exacerbated if the user needs to charge the devices at multiple locations, for example at the home and at the office, or if the user travels often.
One approach to mitigate this problem is the standardization of chargers. For example, a universal charger might be fitted with detachable charging plugs to fit a number of portable devices. The source of power for the charger might be a power line, a computer USB port, a solar cell, a fuel cell or even a mechanically turned dynamo. This approach still results in a duplication of components (the charging plugs).
A further approach, which eliminates the use of charging plugs, is the use of an inductive coupling (magnetic field interaction) to provide a wireless coupling to the portable device. In one approach, a charging pad contains a number of electrical coils that carry an electrical current. The portable device also contains an electrical coil. When the portable device is place on the charging pad, an electrical current is induced in the coil of the portable device; this current is used to charge the battery.
In a second approach, inductive charging is combined with a solar cell. The solar cell receives ambient light and converts it to electricity to slowly charge a battery in the charger. An inductive coupling is used to transfer charge to the portable device when it is placed close to the charger.
While an inductive charger has advantages, one disadvantage is that the electromagnetic field may interfere with other electronic devices, of magnetically recorded media (such as credit cards or video tapes).